Fractured Carbonate Rock Research
According to a 2012 review volume on carbonate exploration and reservoir analysis co-edited by an SDI researcher, it is commonly quoted that carbonate reservoirs contain some 50–60% of the world’s oil and gas reserves (Garland et al., 2012). Indeed, the world’s largest oil field (Ghawar, Saudi Arabia) and the world’s largest gas field (North Field/South Pars straddling the Qatar/Iran border) are both reservoired in carbonate rocks. Many low-matrix-porosity hydrocarbon reservoirs are productive because permeability is controlled by fractures and faults. Understanding basic fracture properties is critical in reducing geological risk and therefore reducing well costs and increasing well recovery.
Research on the origins and controls on fractures in carbonate rocks has been an abiding part of the SDI initiative research program, including work on the regional stratigraphic and diagenetic controls on fracture occurrence (Marrett and Laubach, 2001; Ortega et al., 2013), fracture abundance (Marrett et al., 1999; Ortega et al., 2006), spatial arrangement (Gale, 2002), mechanical and fracture stratigraphy (Laubach et al., 2009), modeling cement accumulation in fractures (Gale et al., 20010), how to image carbonate minerals (Reed and Milliken, 2003), interaction of cement accumulation and fracture growth (Hooker et al., 2012), mechanical properties of carbonate rocks (Olson, 2004), detection of fractures using seismic methods (Marrett et al., 2007), modeling fracture patterns (Olson, 2004) and modeling the role of fractures on reservoir behavior and fluid flow (Philip et al., 2005).
Research on Fractures in Carbonate Rocks
Dr. Esti Ukar has recently undertaken the lead on SDI’s effort in natural fracture research in carbonate rocks. She also directs the new high-resolution field emission scanning electron microscope facility with a focus on cathodoluminescence imaging (SEM-CL).
Ukar’s research combines small-scale brittle structural petrology with large-scale deformation characterization and modeling on the upper continental crust. Ukar’s reseach spans from fracture scaling analyses and fracture evolution and timing modeling using commercial and in-house software, to developing paleostress indicators using twinned fracture cements.
The following papers and abstracts reflect some of Ukar’s current research interests:
- Ukar, E., Eichhubl, P., Laubach, S. E., Hooker, J. N., and Marrett, R., in review, Evidence of a universal fracture size scaling exponent in core and outcrop fracture size distributions, Nikanassin Formation, Alberta Foothills, Canada, and implications for measuring fold-related fracture abundance. AAPG Bulletin.
- Ukar, E., Ozkul, C., Eichhubl, P., and Fall, A., 2014, Structural-diagenetic evolution of fractures in folds: Nikanassin and Cardium Formations, Alberta Foothills, Canada. Abstract presented at AAPG Annual Convention and Exhibition, Houston, Texas, April 7th-9th.
- Ukar, E., and Cloos, M., 2014. Low-temperature blueschist-facies mafic blocks in the Franciscan mélange, San Simeon, California: Field relations, petrology, and counterclockwise PT paths. Geological Society of America Bulletin, B30876-1.
- Ukar, E., Eichhubl, P., Fall, A., and Hooker, J. N., 2013, Structural-diagenetic controls on fracture opening in tight gas sandstone reservoirs, Alberta Foothills. European Geosciences Union General Assembly, 2013, Vienna, Austria. Geophysical Research Abstracts, v. 15, EGU2013-13327.
- Ukar, E., Cloos, M., and Vasconcelos, P., 2012. First 40Ar-39Ar ages from low-T Mafic blueschist blocks in a Franciscan Mélange near San Simeon: Implications for initiation of subduction. The Journal of Geology, 120(5), 543-556.
Carbonate Rock Structural Diagenesis Initiative
In 2014 SDI began a campaign to systematically unravel the structural diagenesis of fracture systems in carbonate rocks, building on our previous work [see reference list below]. The program is led by Ukar, Marrett and Laubach and includes a core group of industry experts. Initial topics of research include
- Timing and rate of fracture growth
- Role of cement in fracture size and spatial arrangement development
- Diagenetic evolution of mechanical and fracture stratigraphy
- Fracture-prone and fracture-resistant rocks (including rock properties library)
- Evolution of fracture porosity and permeability
- Prediction of fracture attributes including clustering, height distribution
- Subsurface (core, log, production & seismic) and outcrop-based studies
- Numerical modeling using JOINTS and other structural modeling approaches
- Review of existing knowledge of fracture systems in carbonate rocks
Progress reports are listed here.
Selected initiative papers on fractures in carbonate rocks:
- Gale, J. F. W. and Gomez, L. A., 2007, Late opening-mode fractures in karst-brecciated dolostones of the Lower Ordovician Ellenburger Group, west Texas: Recognition, characterization, and implications for fluid flow. AAPG Bulletin 91: 1005-1023.
- Gale, J. F. W., 2002, Specifying lengths of horizontal wells in fractured reservoirs: Society of Petroleum Engineers Reservoir Evaluation and Engineering, v. 5, no. 3, p. 266-272.
- Gale, J. F. W., Laubach, S. E., Marrett, R. A., Olson, J. E., Holder, J. & Reed, R. M., 2004, Predicting and characterizing fractures in dolostone reservoirs: using the link between diagenesis and fracturing. In: Braithwaite, C. J. R., Rizzi, G. & Darke, G., eds., The Geometry and Petrogenesis of Dolomite Hydrocarbon Reservoirs. Geological Society, London, Special Publications, 235, 177-192.
- Gale, J.F., Lander, R.H., Reed, R.M., and Laubach, S.E., 2010, Modeling fracture porosity evolution in dolostone. Journal of Structural Geology, v. 32, no. 9, p. 1201-1211. doi:10.1016/j.jsg.2009.04.018.
- Garland, J., J.E. Neilson, S.E. Laubach, & K. J. Whidden, 2012, Advances in carbonate exploration and reservoir analysis. In Garland, J., J.E. Neilson, S.E. Laubach, & K. J. Whidden (eds.) Advances in Carbonate Exploration and Reservoir Analysis, Geological Society of London Special Publications 370, p. 1-15. doi: 10.1144/SP370.15
- Hooker, J.N., Gomez, L.A., Laubach, S.E., Gale, J.F.W. & Marrett, R., 2012, Effects of diagenesis (cement precipitation) during fracture opening on fracture aperture-size scaling in carbonate rocks. In Garland, J., J.E. Neilson, S.E. Laubach, & K. J. Whidden (eds.) Advances in Carbonate Exploration and Reservoir Analysis, Geological Society of London Special Publications 370, p. 187-206. doi:10.1144/SP370.9.
- Benedicto, A., Schultz, R. A., 2010, Stylolites in limestone: magnitude of contractional strain accommodated and scaling relationships. Journal of Structural Geology, 32(9), 1250-1256.
- Laubach, S. E., Olson, J. E., and Gross, M. E., 2009, Mechanical and fracture stratigraphy: AAPG Bulletin, v. 93, no. 11, p. 1413-1426.
- Marrett, R., ed., 2001, Genesis and controls of reservoir-scale carbonate deformation, Monterrey salient, Mexico : The University of Texas at Austin, Bureau of Economic Geology, Guidebook 28.
- Marrett, R., Laubach, S.E. Olson, J.E., 2007, Anisotropy and beyond: geologic perspectives on geophysical prospecting for natural fractures. The Leading Edge, 26/9, 1106-1111.
- Marrett, R., Ortega, O.O., and Kelsey, C., 1999, Extent of Power-law scaling of natural fractures in rock: Geology, v. 27, 799-802.
- Marrett, Randall, and Laubach, S. E., 2001, Fracturing during burial diagenesis, in Marrett, R., ed., Genesis and controls of reservoir-scale carbonate deformation, Monterrey salient, Mexico: The University of Texas at Austin, Bureau of Economic Geology, Guidebook 28, p. 109-120.
- Olson, Jon, 2004, Predicting fracture swarms – the influence of subcritical crack growth and the crack-tip process zone on joint spacing in rock, in Cosgrove, J.W., and Engelder, T., editors, The initiation, propagation, and arrest of joints and other fractures, Geological Society of London Special Publication 231, 73-87.
- Ortega, O. J., Marrett, R., and Laubach, S. E., 2006, A scale-independent approach to fracture intensity and average fracture spacing: AAPG Bulletin, v. 90, no. 2 (Feb. 2006), 193-208.
- Ortega, O.J., Gale, J.F.W., Marrett, R., 2010, Quantifying diagenetic and stratigraphic controls on fracture intensity in platform carbonates: An example from the Sierra Madre Oriental, northeast Mexico, Journal of Structural Geology, v. 32, no. 12, p. 1943-1959. doi:10.1016/j.jsg.2010.07.004.
- Philip, Z. G., Jennings, J. W., Jr., Olson, J., Laubach, S. E., and Holder, Jon, 2005, Modeling coupled fracture-matrix fluid flow in geomechanically simulated fracture networks: Society of Petroleum Engineers, SPE Reservoir Evaluation & Engineering, v. 8, no. 4, p. 300-309.
- Reed, R. M., and Milliken, K. L., 2003, How to overcome imaging problems associated with carbonate minerals on SEM-based cathodoluminescence systems: Journal of Sedimentary Research, v. 73, no. 2, p. 328–332.